The long term objective of the proposed experiments is the production, testing and refinement of a molecular and genetic model for pattern formation in flower development. This will be done by studying in depth the genetics and molecular genetics of a key homeotic gene in the development of flowers of the plant Arabidopsis thaliana. This is the AGAMOUS gene, whose phenotype is the homeotic conversion of the six stamens found in wild type flowers to six petals, and of the ovary normally found in the center of the flower into a whorl of sepals. In addition, the wild type AGAMOUS gene appears to be responsible for the regulation of the amount and pattern of cell division in several flower parts. Since plant development consists only of the two processes of regulated cell division and patterned cellular differentiation (unlike animals, in which cell migration and maternal information play major roles), understanding the activities of the AGAMOUS gene will be a major step in understanding pattern formation in plants. Since this process appears much simpler in plants than in animals, it is to be expected that many aspects of development in plants will not only be of interest in their own right, but also serve as models for the more complex developmental processes of animals. The AGAMOUS gene is already cloned, and its protein product shares substantial homology with a class of transcriptional regulators known in vertebrates and in baker's yeast. The human homologue is Serum Response Factor, which is a key transcriptional regulator of the human c-fos oncogene. This underlies the relatedness of the proposed studies to the health problems of birth defects, caused by abnormal embryonic pattern formation, and of carcinogenesis. The specific aims are to study the action of AGAMOUS and its interaction with a series of additional homeotic genes. Among the proposed experiments are the careful study of the place and time of AG action and expression, by in situ analysis of RNA, by antibody localization of the AG protein, and by expression of reporter genes. All of this will be done in wild type and various mutant backgrounds. In additional a series of experiments to spatially and temporally misexpress the gene are planned, as are genetic mosaic studies. Finally, a detailed study of the newly-discovered family of AG homologues in the Arabidopsis genome will be performed, to learn the activity of the many other plant genes now known to be related to AGAMOUS, and thus to human Serum Response Factor.